Inappropriate activation of leukocytes including monocytes, macrophages and neutrophils leading to the production of elevated levels cytokines such as TNF-α, IL1-β and IL-8, is a feature of the pathogenesis of several inflammatory diseases including rheumatoid arthritis, ulcerative colitis, Crohn's disease, chronic obstructive pulmonary disease (COPD), asthma and psoriasis. The production of cytokines by inflammatory cells is a result of response to a variety of external stimuli, leading to the activation of a number of intracellular signalling mechanisms. Prominent amongst these is the mitogen-activated protein kinase (MAPK) superfamily consisting of highly conserved signalling kinases that regulate cell growth, differentiation and stress responses. Mammalian cells contain at least three families of MAPKs: the p42/44 extracellular signal-regulated kinase (ERK) MAPKs, c-Jun NH2-terminal kinases (JNKs) and p38 MAPK (also termed p38α/Mpk2/RK/SAPK2α/CSBP1/2). p38 MAPK was first cloned following its identification as a kinase that is tyrosine phosphorylated after stimulation of monocytes by lipopolysaccharide (LPS) [Han et al, Science 1994,265,808]. Additional homologues of mammalian p38 have been described and include p38β [Jiang et al, J. Biol. Chem., 1996, 271, 17920], p38γ [Li et al, Biochem. Biophys. Res. Commun. 1996, 228, 334] and p38δ [Jiang et al, J. Biol. Chem. 1997, 272, 30122]. While p38α and p38β are ubiquitously expressed, p38γ is restricted primarily to skeletal muscle and p38δ is predominantly expressed in lung and kidney.
The release of cytokines by host defense cells and the response of leukocytes to cytokines and other pro-inflammatory stresses are to varying extent regulated by p38 MAPK [Cuenda et al, FEBS Lett, 1995, 364, 229-233]. In other cell types, p38 MAPK controls stress responses such as the production of IL-8 by bronchial epithelial cells stimulated by TNF-α, and the up-regulation of the cell adhesion molecule ICAM-1 in LPS-stimulated endothelial cells. Upon activation, via dual phosphorylation of a TGY motif by the dual specificity kinases MKK3 and MKK6, p38 MAPK exerts its effects through phosphorylation of transcription factors and other kinases. MAP kinase-activated protein kinase-2 (MAPKAPK-2) has been identified as a target for p38 phosphorylation. It has been demonstrated that mice [Kotlyarov et al, Nat. Cell Biol. 1999, 1, 94-97] lacking MAPKAPK-2 release reduced levels of TNF-α, IL-1β, IL-6, IL-10 and IFN-γ in response to LPS/galactosamine mediated endotoxic shock. The regulation of the levels of these cytokines as well as COX-2 is at the mRNA level. TNF-α levels are regulated through translational control via AU-rich elements of the 3′-UTR of TNF-α mRNA, with MAPKAPK-2 signalling increasing TNF-αmRNA translation. MAPKAPK-2 signalling leads to increased mRNA stability for COX-2, IL-6 and macrophage inflammatory protein. MAPKAPK-2 determines the cellular location of p38 MAPK as well as transducing p38 MAPK signalling, possessing a nuclear localisation signal at its carboxyl terminus and a nuclear export signal as part of its autoinhibitory domain [Engel et al, EMBO J. 1998, 17, 3363-3371]. In stressed cells, MAPKAPK-2 and p38 MAPK migrate to the cytoplasm from the nucleus, this migration only occurring when p38 MAPK is catalytically active. It is believed that this event is driven by the exposure of the MAPKAPK-2 nuclear export signal, as a result of phosphorylation by p38 MAPK [Meng et al, J. Biol. Chem. 2002, 277, 37401-37405]. Additionally p38 MAPK either directly or indirectly leads to the phosphorylation of several transcription factors believed to mediate inflammation, including ATF1/2 (activating transcription factors 1/2), CHOP-10/GADD-153 (growth arrest and DNA damage inducible gene 153), SAP-1 (serum response factor accessory protein-1) and MEF2C (myocyte enhancer factor-2) [Foster et al, Drug News Perspect. 2000, 13, 488-497].
It has been demonstrated in several instances that the inhibition of p38 MAPK activity by small molecules, is useful for the treatment of several disease states mediated by inappropriate cytokine production including rheumatoid arthritis, COPD, asthma and cerebral ischemia. This modality has been the subject of several reviews [Salituro et al, Current Medicinal Chemistry, 1999, 6, 807-823 and Kumar et al, Nature Reviews Drug Discovery 2003, 2, 717-726].
Inhibitors of p38 MAPK have been shown to be efficacious in animal models of rheumatoid arthritis, such as collagen-induced arthritis in rat [Revesz et al, Biorg. Med. Chem. Lett., 2000, 10, 1261-1364] and adjuvant-induced arthritis in rat [Wadsworth et al, J. Pharmacol. Exp. Ther., 1999, 291, 1685-1691]. In murine models of pancreatitis-induced lung injury, pretreatment with a p38 MAPK inhibitor reduced TNF-α release in the airways and pulmonary edema [Denham et al, Crit. Care Med., 2000, 29, 628 and Yang et al, Surgery, 1999, 126, 216]. Inhibition of p38 MAPK before ovalbumin (OVA) challenge in OVA-sensitized mice decreased cytokine and inflammatory cell accumulation in the airways in an allergic airway model of inflammation, [Underwood et al, J. Pharmacol. Exp. Ther., 2000, 293, 281]. Increased activity of p38 MAP kinase has been observed in patients suffering from inflammatory bowel disease [Waetzig et al, J. Immunol, 2002, 168, 5432-5351]. p38 MAPK inhibitors have been shown to be efficacious in rat models of cardiac hypertrophy [Behr et al, Circulation, 2001, 104, 1292-1298] and cerebral focal ischemia [Barone et al, J. Pharmacol. Exp. Ther., 2001, 296, 312-321].
We have now discovered a group of compounds which are potent and selective inhibitors of p38 MAPK (p38α, β, γ and δ) and the isoforms and splice variants thereof especially p38α, p38β and p38β2. The compounds are thus of use in medicine, for example in the treatment and prophylaxis of immune and inflammatory disorders described herein. The compounds are characterised by the presence in the molecule of an α,α-disubstituted glycine motif or an α,α-disubstituted glycine ester motif which is hydrolysable by an intracellular carboxylesterase. Compounds of the invention having the lipophilic α,α-disubstituted glycine ester motif cross the cell membrane, and are hydrolysed to the acid by the intracellular carboxylesterases. The polar hydrolysis product accumulates in the cell since it does not readily cross the cell membrane. Hence the p38 MAP kinase activity of the compound is prolonged and enhanced within the cell. The compounds of the invention are related to the p38 MAP kinase inhibitors encompassed by the disclosures in International Patent Application WO03076405 but differ therefrom in that the present compounds have the amino acid ester motif referred to above.
The compounds of the invention are also related to those disclosed in our copending International Patent Application No. WO 2007/129040. The latter compounds have an α-monosubstituted glycine ester motif which also enables the compounds to cross the cell membrane into the cell where they are hydrolysed to the corresponding acid by intracellular carboxylesterases. However, that publication does not suggest that α,α-disubstituted glycine ester conjugates can be hydrolysed by intracellular carboxylesterases. In fact, it appears that the ability of the intracellular carboxyl esterases, principally hCE-1, hCE-2 and hCE-3, to hydrolyse α,α-disubstituted glycine esters has not previously been investigated.
The general concept of conjugating an α-mono substituted glycine ester motif to a modulator of an intracellular enzyme or receptor, to obtain the benefits of intracellular accumulation of the carboxylic acid hydrolysis product is disclosed in our International Patent Application WO 2006/117567. However, this publication does not suggest that α,α-disubstituted glycine ester conjugates can be hydrolysed by intracellular carboxylesterases. As mentioned above, it appears that the ability of the intracellular carboxyl esterases, principally hCE-1, hCE-2 and hCE-3, to hydrolyse α,α-disubstituted glycine esters has not previously been investigated.